The present invention relates to a coating for a golf ball. Golf balls are often coated with an outermost protective polyurethane clear coating. Polyurethane systems may be either "one component" systems or "two component" systems. One component systems are generally made up of minute polymeric, reacted or partially reacted particles which are suspended or dispersed in one or more solvents. Curing and subsequent formation of a coating results by evaporation of the solvent(s) and/or addition of a curing agent. Two component systems rely on keeping the primary reactants separate from one another until the time for forming the coating. Upon addition of the reactants to one another, polymerization occurs. In forming a coating, such reaction may be accompanied or followed by evaporation of the solvent(s).
Polyurethane systems may be classified as either water-based or nonaqueous solvent-based systems. Both water-based systems and nonaqueous solvent-based systems may be either one or two component systems. Such nonaqueous systems typically employ relatively high concentrations of one or more organic solvents. In such systems it is generally necessary to exclude water from the reaction environment.
Water-based polyurethane coating compositions offer several advantages over nonaqueous, organic solvent-based systems. Organic solvents are often more expensive than water and often hazardous to work with and so less desirable especially for large scale production operations. Moreover, it is not desirable to store or maintain a supply of organic solvents in view of their relative toxicity and flammability compared to water. In addition, two component water-based systems are generally preferred over one component systems since coatings formed from two component systems generally have superior strength and durability as compared to coatings formed frown one component systems.
Two component water-based polyurethane systems are typically formed from a first component of polyol and water and a polyisocyanate second component. Upon addition of the components to one another and evaporation of water or other solvents from the system, a polymeric urethane coating is formed. Although such two component water-based systems are preferable in many respects to traditional nonaqueous solvent-based systems and one component water-based systems, there are numerous problems in attempting to form a two component, water-based polyurethane top coat on a golf ball.
One problem encountered in forming a polyurethane coating from a two component water-based polyurethane system is that the polyisocyanate readily reacts with water either in the other component or in the surrounding environment, thereby generating carbon dioxide gas which tends to foam the coating. The resulting foamy appearance and rough surface is undesirable and is often accompanied by poor coating properties. Such coatings are unacceptable for use on golf bails. Thus, there is a need for a two component water-based polyurethane golf ball coating which avoids the formation of carbon dioxide or other gaseous agent(s) during formation and application of the coating, and which produces a clear, protective, aesthetically pleasing golf ball top coat.
In addition, it is necessary that any outer coating applied to a golf ball not destroy or significantly alter the particular surface configuration of the golf ball. An outer coating which destroys or significantly alters the surface configuration of a golf ball generally adversely affects the aerodynamics of the ball. Coating compositions which have a relatively high viscosity tend to form coatings having varying thicknesses especially when such coatings are applied onto special irregular surfaces such as that formed into a golf ball. Thus, prior to application of a coating composition to a golf ball, it may be necessary to adjust the viscosity of the composition by addition of a solvent. As noted, it is undesirable to utilize nonaqueous organic solvents in view of their cost, health hazards, toxicity and flammability. In water-based systems, the addition of water promotes time generation of carbon dioxide to produce a foamy coating. Thus, there is a need for a golf ball coating having a viscosity which may be readily adjusted by the addition of water while avoiding foaming.
As far as is known, all golf ball top coats for SURLYN.RTM. covered golf balls (the majority of all golf balls currently produced) require a primer coat or adhesion promoting layer deposited on the SURLYN.RTM. material. The expense of primer or adhesion promoting materials is undesirable especially in commercial manufacturing operations. In addition, the application of a primer coat or adhesion promoting layer significantly adds to the labor, time, and effort in producing a golf ball. Thus, there is a need for a golf ball top coat for a SURLYN.RTM. covered golf ball which does not require a primer coat or adhesion promoting layer.